I read the reviews for my fanfiction series, and respond to them. My attitude to reading anything, either fanfic or published works is rather 'Don't like, don't read,' however. Fanfic is rather different to published works, though in that we are obliged on most archives to warn for adult situations, violence, rape, M/M, F/F, fetish, etc, so if a reader looks at all those warnings, hates those subjects and still reads them -- well, *boggles*, I just don't understand that mentality.
Picking up a published book, unless it's clearly GBLTQ (Gay, Bi, Lesbian, Transgender, Queerfolk) literature, we have very little idea what is going to be in it. (I read some horrendously-written soft-porn bodice-rippers from about 11 onward, because they masqueraded as romance. )
I think author's primarily write for themselves. That is not to say that if some-one who follows my series would like to see more of a certain character, pairing, or plot idea, I don't take any notice; I do, if it can be written to flow in with the existing plot. But I always think that if a reader finds something they do not like, then rather than spend time writing about it, *they* should go and write something they *do* like. It's far more creative. Were I following an author who suddenly started writing stories that I felt were poor, or no longer interesting, I would just drop them. There are always more authors and books to read.